Not applicable.
Not applicable.
1. Field of the Invention
The present invention relates generally to the field of navigation, and, more particularly, to a system for controlling movement of a free-ranging vehicle on a surface. Although the present invention is subject to a wide range of applications, it is especially suited for use in a vehicle-ride attraction of an entertainment park, and will be particularly described in that connection.
2. Description of the Related Art
Automatically guided vehicles require some method of determining their location so that they can achieve the position/time/velocity profile desired. Existing methods include the use of the Global Position System (GPS), differential radio triangulation, laser triangulation, wheel encoders, Inertial Navigation Systems (INS) and others. Each of these methods have deficiencies which either increase costs, limit performance, or inhibit the environment in which the vehicle system can be used.
In addition, the ride vehicles may move through an extremely varied environment which may include large vertical structures, other moving objects, as well as special effects and projections emitting light, heat, and electromagnetic fields which could interfere with position location systems which depend on line-of-sight paths between vehicles and wayside emitters or sensors. However, a well-controlled interface between the vehicle and the floor is usually available.
An example of a navigation system for use with a free-ranging vehicle is described in U.S. Pat. No. 4,847,773 to van Helsdingen et al. (van Helsdingen ""773 patent). The van Helsdingen ""773 patent discloses a navigation system for use with a free-ranging vehicle that utilizes a detector for reading passive markers embedded in a floor to determine the vehicle""s position.
In particular, the van Helsdingen ""773 patent discloses a grid of passive markers which are positioned on, or in, a floor surface having a certain layout, which provides a grid over which the vehicle can move. The vehicle includes wheels, a motor for driving the wheels, and a steering mechanism for the wheels. The navigation system of the vehicle includes detectors for detecting the passive markers as the vehicle passes over them. The passive markers provide intermittent marker detection signals. The detector irradiates the passive marker which returns a signal merely indicating the presence of the marker.
Further, a computer control unit is connected to the steering mechanism and the detectors. The computer control unit computes a planned path for the vehicle over the floor surface, from a known starting point to an arbitrary destination, based upon stored information regarding the layout and the grid. Thus the vehicle knows when to expect to travel over which particular grid element in advance. The progress along the pre-computed path is frequently checked when passing over markers and, if necessary, the actual path is adjusted to correct for deviations in the movement of the vehicle from the planned path.
Although suitable for some free-ranging vehicles where the vehicle""s starting position is known and the path of the vehicle is preplanned point-to-point route, this navigation system is not suitable for free-ranging vehicles that begin their travel from unknown starting points and whose destination point, and thus route, can be changed during the course of travel.
A need therefore exists for a system for controlling movement of a free-ranging vehicle on a surface that enables the vehicle to begin its travel from starting points not known in advance and whose destination point, and thus route, can be changed during the course of travel.
The present invention, which tends to address this need, resides in a system for controlling movement of a free-ranging vehicle on a surface. The system described herein provide advantages over known navigation systems in that it enables the vehicles to begin their travel from starting points not known in advance and whose destination point, and thus route, can be changed during the course of travel. It does so by utilizing an interface between the vehicle and the surface the vehicle traverses and correcting its course based on absolute position readings.
According to the present invention, the system corrects vehicle motion command signals for errors caused by drift of an onboard dual-axial inertial sensor based on the comparison of the absolute position and the absolute orientation of a vehicle and the estimated position and the estimated orientation of the vehicle. This can be accomplished by at least two dual-axial sensors, mounted to the vehicle, that provide continuous acceleration data; a plurality of tags, fixedly arranged about the surface, that provides absolute location data; at least two tag readers, mounted to the vehicle, each to read the absolute location data of the respective tags that the at least two tag readers pass over as the vehicle moves about the surface; and a computer, mounted to the vehicle, functioning to receive the absolute location data and the acceleration data, compare the absolute position and the absolute orientation to the estimated position and the estimated orientation; and a vehicle navigation system for controlling the motion of the vehicle based on the corrected motion command signals. Thus, the vehicle can begin its travel from starting points not known in advance and can change its route during the course of travel.
In accordance with one aspect of the present invention, the plurality of tags are arranged in a rectilinear grid of equally spaced rows and columns. This arrangement provides a cost-effective and easily installed tag grid.
In accordance with another aspect of the present invention, the plurality of tags are arranged in a grid of alternating off-spaced columns. The resulting array is such that the distance between tags is constant. This arrangement provide some advantage in that the distance the vehicle must move to encounter a new tag is constant regardless of direction.
In accordance with still another aspect of the present invention, the at least two tag readers and the plurality of tags are arranged such that only one tag is read by a single tag reader at a time. This feature allows the tag reader to uniquely distinguish a tag during reading.
In accordance with a further aspect of the present invention, the velocity and acceleration of the vehicle is computed based on successive readings of the absolute location data made by the at least two tag readers at different vehicle positions. Position, velocity and acceleration can be computed from both the absolute location data from the at least two tag readers and the acceleration data from the at least two dual-axis sensors. The acceleration-based sensors provide higher accuracy and resolution but only for a short time before measurement drift becomes excessive. The system computes a running average from the absolute location data that can be used alone in slower, lower resolution applications or used to correct the acceleration-based measurements. The combination of acceleration-based sensors and tag readers can provide continuous high accuracy and resolution position, velocity, and acceleration for the vehicle control system. Also, if the acceleration-based sensors fail or are otherwise unusable, the system may use the tag readers alone as a lower resolution backup.
In accordance with another aspect of the present invention, at least one tag is read by the array of tag readers when the vehicle is stopped. This can be accomplished by having a one of the at least two tag readers include an array of tag readers that overlap so that at least one tag is in range of the tag reader. Thus, a vehicle which moves in random paths with respect to tag geometry, or which must know its position without movement upon power up in any location, can obtain absolute position data.
In accordance with still another aspect of the present invention, upon vehicle startup, the vehicle makes a series of short moves until a one of the at least two tag readers reads the absolute location data of the respective tag that the one of the at least two tag readers passes over as the vehicle moves about the surface. In this way, an absolute starting position can be obtained. The movements can continue until two tag readers read their respective tags, thereby establishing the vehicle""s orientation.
In accordance with a further aspect of the present invention, the plurality of tags are passive radio-frequency identification (RFID) tags and the at least two tag readers are RFID tag readers. These types of tags and readers are low cost, low maintenance, and highly reliable. Moreover, their close proximity and 13.56 megahertz frequency minimize interference from other sources of energy, and the tags are simply installed by typical building contractors.
In accordance with another aspect of the present invention, the absolute location data is a unique code assigned to each tag. The computer stores a table juxtaposing the unique codes and the absolute location of the tags about the surface and translates the read unique code into the absolute location of the respective tag. In this way, the installation of the tags is simplified.
In accordance with another aspect of the present invention, the absolute location data is an identification assigned to each tag representing the x-y coordinates of the absolute location of each tag. This serves to greatly simplify and reduce the computation time of the table look up step by the computer.
In accordance with still another aspect of the present invention, the at least two tag readers can write a signature of the vehicle and the plurality of tags are writeable tags. Thus, the vehicle can leave a signature of itself on the plurality of tags that the at least two tag readers pass over as the vehicle moves about the surface. This has the advantage that a vehicle can mark its territory in a game playing situation.
Other features and advantages of the present invention will be set forth in part in the description which follows and accompanying drawings, wherein the preferred embodiments of the present invention are described and shown, and in part become apparent to those skilled in the art upon examination of the following detailed description taken in conjunction with the accompanying drawings, or may be learned by practice of the present invention. The advantages of the present invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.